Bedform development in confined and unconfined settings of the Carchuna Canyon (Alboran Sea, western Mediterranean Sea): An example of cyclic steps in shelf-incised canyons

IF 2.6 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology Pub Date : 2024-11-07 DOI:10.1016/j.margeo.2024.107429

J. Cerrillo-Escoriza , A. Micallef , F.J. Lobo , Á. Puga-Bernabéu , P. Bárcenas , I. Schulten , R. Durán , Á. Carrión-Torrente , A. López-Quirós , M. Luján , O. Sánchez-Guillamón , M.J. Sánchez

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引用次数: 0

Abstract

Newly acquired high-resolution multibeam bathymetry in combination with sub-bottom acoustic profiles, surficial sediment samples, and three-dimensional flow simulations made possible the characterization of bedforms along the axial channel and depositional lobe of the shelf-incised Carchuna Canyon (Alboran Sea, western Mediterranean Sea). This study aims to describe the erosional and depositional bedforms in confined and unconfined settings of the Carchuna Canyon in order to determine the genetic constraints on sedimentary processes leading to bedform development along the canyon in recent times.

The straight Carchuna Canyon, deeply incised in the shelf up to 200 m off the coastline, hosts: (1) crescentic-shaped bedforms (CSBs) that exhibit distinctive crest concavities, asymmetries, and lengths along the axial channel; (2) continuous lateral levees and; (3) a channel bend with three depressed stretches of the levee crest that are less than 20 m high. A set of concentric sediment waves and two scour trails were identified proximal to the channel bend over an overbank deposit east of the Carchuna Canyon. Four acoustic units with distinct acoustic facies were defined along the sediment wave field. The sediment transport simulation shows the highest flow velocities along the Carchuna Canyon thalweg, while over the overbank deposit the highest velocity values occur along the top of the bedform crests, with the higher Froude values being found over bedform lee sides.

The occurrence of CSBs along the canyon axial channel suggests the imprint of confined sediment-laden gravity flows descending from the canyon head and exhibiting a flow variability along the canyon induced by local variations of slope gradient and/or sediment concentration. A spatial relationship is identified between the development of sediment waves over the overbank deposit and lowered levee crest heights at the channel bend. In contrast, more energetic downstream turbiditic flows exceed the levee crest at the channel bend, focusing the overflow and promoting erosion of the overbank deposit, thereby generating the scour trains. Based on the recent history of overbank deposition, two alternating scenarios of flow behavior can be interpreted. In a high-density turbidity current setting, erosion would prevail along the axial channel. Widespread spillover flows of coarse-grained sediments would occur in both levees, forming heterogeneous sedimentary patterns that change downslope within the depositional lobe due to lesser turbulence of spillover turbidity currents and gentler slope gradients. In contrast, in a low-density turbidity current setting, turbidity currents flowing along the Carchuna Canyon would form depositional bedforms in the axial channel, while spillover processes would be localized at the channel bend, forming either depositional or erosional bedforms over the depositional lobe according to the frequency, magnitude and focusing of turbiditic flows.

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卡丘纳峡谷（地中海西部阿尔博兰海）封闭和非封闭环境中的床形发展：陆架封闭峡谷循环阶梯的一个实例

新近获得的高分辨率多波束测深数据与海底声学剖面图、表层沉积物样本和三维流动模拟相结合，使沿陆架嵌入的卡丘纳峡谷（地中海西部阿尔博兰海）轴向河道和沉积叶的床形特征得以确定。这项研究旨在描述卡丘纳峡谷封闭和非封闭环境中的侵蚀和沉积床面形态，以确定导致峡谷床面形态发展的沉积过程在近代的遗传制约因素。笔直的卡丘纳峡谷深深切入离海岸线 200 米的大陆架，峡谷内有：(1) 新月形河床（CSBs），沿轴向河道呈现出独特的峰顶凹陷、不对称和长度；(2) 连续的横向堤坝；(3) 河道弯曲，堤坝峰顶有三段凹陷，高度不足 20 米。在卡丘纳峡谷以东的过岸沉积物上，在河道弯曲处附近发现了一组同心沉积物波浪和两条冲刷路径。沿沉积物波场确定了四个声学单元，它们具有不同的声学面貌。沉积物运移模拟结果表明，沿卡尔丘纳峡谷干流的流速最高，而在两岸沉积物上，最高流速值出现在基岩峰顶，而较高的 Froude 值则出现在基岩坡面。在河道弯曲处，过岸沉积物波浪的发展与堤顶高度降低之间存在空间关系。与此相反，能量更大的下游浊流会超过河道弯曲处的堤顶，集中溢流并促进对岸坡沉积物的侵蚀，从而产生冲刷列车。根据最近的过岸沉积历史，可以解释两种交替出现的水流行为。在高密度浊流环境下，沿轴向河道的侵蚀将占主导地位。粗颗粒沉积物的大范围溢出流将出现在两个堤坝上，形成异质沉积模式，由于溢出浊流的湍流较小，坡度较缓，沉积叶内的沉积模式会向下变化。相反，在低密度浊流环境中，沿卡丘纳峡谷流动的浊流将在轴向河道中形成沉积床形，而溢出过程将集中在河道弯曲处，根据浊流的频率、大小和集中程度，在沉积叶上形成沉积或侵蚀床形。

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来源期刊

Marine Geology 地学-地球科学综合

CiteScore

6.10

自引率

6.90%

发文量

175

审稿时长

21.9 weeks

期刊介绍： Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.